Back to cannabis and psychosis

A new study that found that daily use of cannabis (or use of high potency cannabis) greatly increased risk of "first time" psychosis.   Hardly seems surprising, really, but it's another reminder of how medical understanding can take a long time to catch up with lay persons' real life observations:

Dr. Robin Murray, senior author of the study and a professor of psychiatric research at the Institute of Psychiatry, Psychology & Neuroscience at King's College London, said that "15 years ago nobody thought cannabis increased the risk for psychosis." 

 

Only gradually has evidence come out and shown that to be true, he said. Gradually, too, other explanations have been chipped away, he said: For example, some people might say that perhaps a genetic predisposition to schizophrenia led some people to use cannabis and this is the reason for higher rates of psychosis. But a study from Finland rules this out, said Murray: "There may be some genetic component but it's not the major reason."

Not for the first time, I wonder out loud:  if governments are going to legalise it, why can't they also regulate for potency too?  If you can't (for good reason) hold a liquor licence and pour spirits into the open mouths of customers due to it being a dangerous way to consume alcohol, why can't you legislate for the potency and likely dosage of cannabis too?